Machines for making seamed tubes are used in making shells for mufflers for motor vehicles.
The muffler manufacturing industry demands a high degree of productivity from this equipment both to meet the demand and the competitive pricing of the finished product. In addition to this however the industry, especially the replacement parts industry, is faced with a very large variety of sizes and shapes of mufflers which results in considerable non-productive cost in time and money to constantly change the tooling over from the production of one size or shape to another.
The shell of a muffler is usually made from one or more sheets of relatively thin sheet steel, stainless or carbon, by a process of forming the sheet around a fixed mandrel by means of a moving form die which conforms in shape to the lower half of the muffler and a moving carriage carrying forming rolls and other tooling which completes the wrap around and forms a mechanical lockseam.
The moving form die has had to be made separately for each form of mandrel for each of the various cross-sectional shapes of mufflers required. Moreover, even when tubes of the same cross-sectional shape are required, it is sometimes the case that the thickness of the material from which they are formed is different. Ideally different dies would be used for different thicknesses of material for tubes of the same shape but usually a die suitable for the greatest thickness is used, thus leading to some inaccuracy.
The action between such dies and the mandrel is a clamping squeezing action which can result in creases in the formed metal.
It is an object of the present invention to obviate the disadvantage of known systems.